Treatment apparatus for operatively correcting defective vision of an eye, method for generating control data therefor, and method for operatively correcting defective vision of an eye

ABSTRACT

A treatment device for the surgical correction of hyperopia in the eye comprising a laser device controlled by a control device. The laser device separating corneal tissue by applying laser radiation. The control device controls the laser device for emitting the laser radiation into the cornea such that a lenticule-shaped volume is isolated. Removal thereof effects the desired correction. The control device predefines the volume such that a posterior surface and an anterior surface are connected via an edge surface that has a width in projection along the visual axis that is wider than the one which a straight line in the same projection, that is perpendicular at the edge of the posterior or the anterior surface would have relative to the associated surface and connects the anterior surface to the posterior surface or to the perceived extension thereof.

RELATED APPLICATION

This application is a continuation of application Ser. No. 16/426,836filed May 30, 2019, which is a continuation of application Ser. No.14/804,922, filed Jul. 21, 2015, which is a division of application Ser.No. 12/742,194, filed Sep. 3, 2010, now U.S. Pat. No. 9,084,666, issuedJul. 21, 2015, which is a National Phase entry of PCT Application No.PCT/EP2008/009076, filed Oct. 27, 2008, which claims priority fromGerman Application No. 102007053283.2, filed Nov. 8, 2007, each of whichis hereby fully incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to a treatment apparatus for surgical correctingdefective vision in the eye, the treatment apparatus having a laserdevice which is controlled by a control device and separates cornealtissue by applying laser radiation, the control device being adapted tocontrol the laser device for emitting the laser radiation into thecornea in such a way that a lenticular volume is thus isolated in thecornea, the removal of which from the cornea effects the desiredcorrection.

The invention further relates to a method for generating control datafor a laser device of a treatment apparatus for operatively correctingdefective vision in the eye, which laser device separates corneal tissueby applying laser radiation, wherein the control data control duringoperation the laser device for emitting the laser radiation into thecornea in such a way that a lenticular volume is thus isolated in thecornea, the removal of which from the cornea effects the desiredcorrection.

Finally, the invention relates to a method for operatively correctingdefective vision in the eye, corneal tissue being separated and alenticular volume thus being isolated and removed in the cornea, theremoval of which from the cornea effects the desired correction, byapplying laser radiation.

BACKGROUND OF THE INVENTION

The conventional way to correct defective vision of the human eye is apair of spectacles. However, meanwhile use is also increasingly beingmade of refractive surgery which effects a correction of defectivevision by altering the cornea of the eye. The aim of the operatingmethods is in this case to alter the cornea selectively in order toinfluence the refraction of light. Different surgical methods are knownfor this purpose. Most widespread at present is what is known aslaser-assisted in situ keratomileusis, which is also abbreviated toLASIK. In this case, a corneal lamella is firstly detached from thesurface of the cornea on one side and folded to the side. This lamellacan be detached by means of a mechanical microkeratome or else by meansof what is known as a laser keratome, such as is sold by Intralase Corp.Irvine, USA, for example. Once the lamella has been detached and foldedto the side, the LASIK operation provides the application of an excimerlaser which removes by ablation the corneal tissue exposed in this way.Once the volume positioned in the cornea has been vaporised in this way,the corneal lamella is folded back to its original site.

The application of a laser keratome to expose the lamella isadvantageous, as this reduces the risk of infection and increases thequality of the cut. In particular, the lamella can be produced at a verymuch more constant thickness. The cut is also potentially smoother; thisreduces subsequent optical disturbances caused by this interface whichremains even after the operation.

When generating a cut face in the cornea by laser radiation,conventionally pulsed laser radiation is introduced into the tissue, thepulse length being generally less than 1 ps. As a result, the powerdensity, which is necessary for triggering an optical breakthrough, forthe respective pulse is confined to a small spatial area. In thisregard, U.S. Pat. No. 5,984,916 clearly discloses that the spatialregion of the optical breakthrough (in this case the interactiongenerated) highly depends on the pulse duration. A high focusing of thelaser beam in combination with the aforementioned short pulses thusallows the optical breakthrough to be employed with pinpoint accuracy inthe cornea. For generating the cut, a series of optical breakthroughs isgenerated at predetermined points in such a way that the cut surface isformed as a result. In the aforementioned laser keratome, the cutsurface forms the lamella which is to be folded down before the use ofthe laser ablation.

In the conventional LASIK method, exposed corneal tissue is vaporised;this is also referred to as “grinding” of the cornea by means of laserradiation. The removal of volume that is necessary for correctingdefective vision is in this case set for each surface element of theexposed cornea by the number of laser pulses and the energy thereof.Different amounts of material are removed in accordance with the numberand energy of the laser pulses.

SUMMARY OF THE INVENTION

Very recently, the operating method mentioned initially has beendescribed and examined in first tests. Laser radiation is used toisolate a volume in the cornea and then to remove the piece of tissueforming this volume. As pulsed laser radiation is generally used in thiscase too, reference is made to femtosecond lenticule extraction or FLExfor short. The volume is referred to as the lenticule.

Now, experimental values which are suitable for grinding the cornea bymeans of ablation laser radiation cannot be used for the FLEx method ofrefractive eye surgery, in which the volume to be removed from thecornea is not removed by the ablation of exposed corneal tissue, but isisolated in the cornea by a three-dimensional cut face and thus madesuitable for removal, as the approaches of vaporising material to beremoved, on the one hand, and removing an isolated volume, on the otherhand, are too different. This applies most particularly to the selectionof the cut surface bounding the volume to be removed, as there is nosuch cut surface in the conventional LASIK operation. The healingprocesses after the operation are also different, as the faces havedifferent surface structures.

Manual removal requires a certain mechanical stability of the piece oftissue that is, in addition to the intended refractive effect, a furtherrequirement. From this point of view, the piece of tissue shouldtherefore be designed to be just as thick as the remaining thickness ofthe cornea, which is set after the removal of the piece of tissue, stillallows.

This desire is opposed by the requirement for shaping allowing therefractive effects of the healing processes to be minimized or at leastto be made predictable. That is to say, if the lenticules are shaped insuch a way that healing processes contribute to a considerable degree tothe alteration of the correction which is directly caused by therefractive therapy, for example as a result of a thickening of thecornea, then the patients would feel this to be disadvantageous. Suchnegative influences of healing processes are referred to as regression.It is necessary to have healing processes proceed with as littleregression as possible, i.e. without refractive alterations; in otherwords: the refractive effect is to occur as rapidly as possible to thedesired extent and then remain constant at all times. However, this isnot always possible, so that the regression associated with healingprocesses often has to be factored into the planning of a refractivetherapy. On account of physiological properties of the human eye, it isto be expected that hyperopic corrections by means of the FLEx methodcan generally be influenced more intensively by healing processes ofthis type. If these refractive changes in the course of the healingprocesses cannot be avoided altogether, it is therefore desirable atleast to make them as slight and predictable as possible.

The prior art does not offer any assistance in this regard incorrections of hyperopia, as the previously known cut and lenticuleshapes relate to corrections of myopia.

Overall, there are thus in many areas different and in some cases alsonew requirements in the refractive correction of defective vision bymeans of FLEx compared to in the conventional LASIK method.

It is therefore the object of the present invention to provide atreatment apparatus or a method of the type mentioned at the outset insuch a way that the cut faces for the lenticule are advantageous bothfor secure removal and for the healing process.

According to the invention, this object is achieved by a treatmentapparatus for surgically correcting hyperopia in an eye, the treatmentapparatus having a laser device which is controlled by a control deviceand separates corneal tissue by applying laser radiation, the controldevice being adapted to control the laser device for emitting the laserradiation into the cornea in such a way that a lenticular volume is thusisolated in the cornea, the removal of which from the cornea effects thedesired correction of hyperopia, wherein the control device, whencontrolling the laser device, defines the lenticular volume in such away that the lenticular volume has a posterior face and an anteriorface, the edges of which are connected via an edge face, wherein a cutcurve made up of the edge face and a plane in which an axis of vision ofthe eye lies having transversely to the axis of vision a width which isgreater than that which would have in the same projection plane astraight line which is perpendicular at the edge of the posterior or theanterior face on the respective face and connects the anterior face tothe posterior face or to the notional continuation thereof.

This object is further achieved by a method for generating control datafor a laser device of a treatment apparatus for operatively correctinghyperopia in an eye, which laser device separates corneal tissue byapplying laser radiation, wherein during operation the control datacontrol the laser device for emitting the laser radiation into thecornea in such a way that a lenticular volume is thus isolated in thecornea, the removal of which from the cornea effects the desiredcorrection of hyperopia, wherein the control data define the lenticularvolume in such a way that it has a posterior face and an anterior face,the edges of which are connected via an edge face, wherein a cut curvemade up of the edge face and a plane in which an axis of vision of theeye lies having transversely to the axis of vision a width which isgreater than that which would have in the same projection plane astraight line which is perpendicular at the edge of the posterior or theanterior face on the respective face and connects the anterior face tothe posterior face or to the notional continuation thereof.

Finally, the object is also achieved by a method for surgicallycorrecting hyperopia in an eye, corneal tissue being separated byapplying laser radiation and a lenticular volume thus being isolated andremoved from the cornea, the removal of which volume effects the desiredcorrection of hyperopia, wherein the lenticular volume is provided witha posterior face and an anterior face, the edges of which are connectedvia an edge face, wherein a cut curve made up of the edge face and aplane in which an axis of vision of the eye lies having transversely tothe axis of vision a width which is greater than that which would havein the same projection plane a straight line which is perpendicular atthe edge of the posterior or the anterior face on the respective faceand connects the anterior face to the posterior face or to the notionalcontinuation thereof.

The invention is based on the finding that postoperative (regression)problems in the FLEX method derive from the fact that the detached andreapplied corneal lamella is disadvantageously inserted or cannot restsmoothly at the edge of the removed volume. In order to avoid regressionproblems of this type, the invention provides a wide edge zone, thusproducing for the corneal lamella, which merges there with the posteriorcut face which was produced for isolating the lenticular volume, atransition zone causing almost no regression. If this transition zone ispreferably also positioned outside the optically effective region, i.e.outside the dark-adapted pupil of the eye, the risk of furtherundesirable side effects is further reduced. Preferably, the transitionzone has a width of between 0.1 and 1 mm.

It has further been found that regressions are particularly effectivelyreduced if the edge face opens as perpendicularly as possible into theanterior face. A course of this type is primarily surprising as, in thecase of a perpendicular opening of this type, a step leadingperpendicularly away from the front face of the cornea can also beprovided for the corneal lamella positioned thereabove. However, thisperpendicular opening has proven unproblematic with regard to regressionif the edge face has a second portion, inclined more intensively towardthe axis of vision, below this perpendicular opening. As a result ofthis structure, the lenticular volume has an edge thickness which ispreferably between 5 and 10 μm. It has been found that an edge thicknessof this type is unproblematic with regard to regression, but at the sametime ensures that the piece of tissue can be removed more effectively,as the edge thickness prevents with sufficient certainty particles frombecoming torn off from the edge when the piece of tissue is detached.Particles of this type influence the positioning of the corneal lamellaafter removal of the tissue much more intensively than does thecomparatively lower edge thickness of the piece of tissue and thus theshort, perpendicularly opening portion of the edge face. Thisconfiguration of the invention therefore takes an edge structure whichat first sight appears negative and achieves therewith as a result lowerregression, i.e. better ingrowth behavior, than an edge which is asnarrow as possible which kind of edge actually would have been expected.

The second portion of the edge face, which is inclined more intensivelytoward the axis of vision, can be embodied in many ways. One possibleexample is a straight course which runs at an angle to the first portionand is positioned at an angle of from 80° to 100° relative to thedirection of the axis of vision. The second portion of the edge face canthen be understood to be a chamfer. However, curved courses are alsopossible, for example a concave course based on the point of passage ofthe axis of vision, i.e. a curvature of the second portion toward theaxis of vision. In this case, the second portion is then designed in theform of a rounding, for example.

Within the scope of the invention, a broad range of geometries aresuitable for the edge that all positively influence the regressionbehavior by providing the described wide transition zone.

In an embodiment of the invention, the edge structure is combined with adimensioning rule for the volume of the cornea that defines the radiusof curvature which the cornea has after the removal of the volume. Thisdevelopment of the invention therefore allows not only aregression-optimized edge structure, but also an analytical calculationof the posterior and the anterior face.

The description of the curvature of the front surface of the corneaafter the correction starts in this case from defective vision datawhich specify the refractive power B_(BR) of a pair of spectacles whichare suitable for correcting defective vision and must be positioned at adistance chis before the corneal apex in order to achieve the desiredcorrection of defective vision. The determining of these parameters isan established standard in ophthalmology and allows the use of existingmeasuring appliances. It goes without saying that the measurement dataused in this case can also represent astigmatism defects or defects ofhigher aberration orders, so that the equation for describing the radiusof curvature of the cornea reduced by the volume then has correspondingangle parameters (based on cylindrical coordinates) as represented inthe following Equation (1) of the description of the figures.

Preference is therefore given to an embodiment of the apparatusaccording to the invention or the method according to the invention inwhich the anterior face is positioned at a constant distance d_(F) fromthe front surface of the cornea and the posterior face is curved and hasa radius of curvature R_(L)=R_(CV)*−d_(F), wherein R_(CV)* satisfies thefollowing equation R_(CV)*=1/((1/R_(CV))+B_(BR)/((n_(c)−1)(1−d_(HS)·B_(BR))))+F, and R_(CV) is the radius of curvature of thecornea before removal of the volume, n_(c) is the refractive index ofthe material of the cornea, F is a correction factor, B_(BR) is therefractive power of a pair of spectacles suitable for correctingdefective vision, and also this is the distance at which the pair ofspectacles having the refractive power B_(BR) would have to bepositioned before the corneal apex in order to achieve the desiredcorrection of defective vision by means of the pair of spectacles.

The correction factor F is a measure of the optical effect of thereduction in thickness of the cornea of the eye on the axis of visionresulting from the removal of the volume. In a simplified calculation,the factor F may be set to zero. In a more accurate calculation, F maybe calculated as follows: F=(1−1/n_(c)) (d_(C)*−d_(C)), wherein d_(C)and d_(C)* respectively denote the thickness of the cornea before andafter removal of the volume and the radius R_(CV)* can be calculatediteratively in that during each iteration step a change in thickness(d_(C)*−d_(C)) is concluded from the difference (R_(CV)*−R_(CV)) and thecorresponding result obtained therefrom for the change in thickness isapplied in the calculation of R_(CV)* in the next iteration step. Theiterative calculation for F can for example be terminated if adifference which is less than a specific limit value is all that remainsfor F between two iteration steps.

The configuration, provided in the embodiment, of the posterior facehaving a curvature which relates to that of the front surface of thecornea after the removal of the volume allows a particularly simpledefinition of the faces bounding the volume, as the anterior face is nowpositioned at a constant distance below the front surface of the corneaand the optical correction is effected by the shape of the posteriorface. Notable computing effort then occurs only for the definition ofthe posterior face part, but not for the anterior face part.Furthermore, it has also been found that an approach of this type allowsat the same time a simple analytical description of the posterior facepart.

The method according to the invention for preparing the control data canbe carried out without human participation. In particular, it can beexecuted by a computer which determines the control data from properinputs, for example from measurement data of the eye. The participationof a doctor is in no way required above all when determining the controldata, as no therapeutic intervention is as yet associated withdetermining the control data. Such intervention does not take placeuntil the previously determined control data are applied.

In so far as this description has described method steps, the apparatusaccording to the invention contains a controller which takes care of theexecution of the method steps during operation of the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail hereinafter by way ofexample with reference to the drawings, in which:

FIG. 1 is a schematic illustration of a treatment apparatus or atreatment device for correcting defective vision;

FIG. 1A is a schematic illustration with regard to the construction ofthe treatment appliance of FIG. 1;

FIG. 2 is an illustration showing the principle for introducing pulsedlaser radiation into the eye in the correction of defective vision usingthe treatment device of FIG. 1;

FIG. 3 is a further schematic illustration of the treatment device ofFIG. 1;

FIG. 4 shows in subfigures (A), (B) and (C) schematic sectionalillustrations to clarify the need for correction in the human eye in thecase of defective vision;

FIG. 5 is a schematic sectional illustration through the cornea of theeye illustrating a volume to be removed for correcting defective vision;

FIG. 6 is a section through the cornea of the eye after removal of thevolume of FIG. 5;

FIG. 7 is a sectional illustration similar to FIG. 5;

FIG. 8 is a schematic sectional illustration through the cornea of theeye to depict the removal of the volume;

FIG. 9A is a plan view onto the cornea of the eye to depict the cutfaces generated during the correction of the defective vision;

FIG. 9B is a sectional illustration relative to the plan view of FIG.9A, depicting the profile of a volume removed for the correction ofhyperopia;

FIG. 10A is an illustration similar to FIG. 9A, but in this case for acorrection of myopia;

FIG. 10B is an illustration similar to FIG. 9A, but again for correctionof myopia;

FIG. 11A is an illustration similar to FIG. 9A, but with a differentguidance of the cut with respect to the removal of the volume;

FIG. 11B is a sectional illustration similar to FIG. 9B, but for theplan view of FIG. 11A;

FIG. 12A is a sectional illustration similar to FIG. 9A, but with adifferent type of edge cut for bounding the volume which is removed forthe correction of defective vision;

FIG. 12B is an enlarged partial view of the edge cut of FIG. 9A; and

FIGS. 12C and 12D are enlarged edge cut illustrations similar to FIG.12B, but for different geometries of the edge face.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a treatment device 1 for an ophthalmic surgical methodsimilar to that described in EP 1159986 A1 or U.S. Pat. No. 5,549,632.The treatment device 1 effects a correction of defective vision in aneye 3 of a patient 4 by means of a treatment laser radiation 2. Thedefective vision may include hyperopia, myopia, presbyopia, astigmatism,mixed astigmatism (astigmatism involving hyperopia in one direction andmyopia in a direction lying at right angles thereto), aspherical defectsand higher-order aberrations. The treatment laser radiation 2 is appliedin the described embodiment as a pulsed laser beam focused into the eye3. The pulse duration is in this case in the femtosecond range, forexample, and the laser radiation 2 acts by means of non-linear opticaleffects in the cornea. The laser beam has for example 50 to 800 fs-shortlaser pulses (preferably 100-400 fs) having a pulse repetition frequencyof between 10 and 500 kHz. In the example embodiment described, theassemblies of the device 1 are controlled by an integrated control unit,although this unit can of course also be embodied in a stand-alonemanner.

Before the treatment device is used, the defective vision of the eye 3is measured using one or more measuring devices.

FIG. 1A shows schematically the treatment device 1. In this variant, thetreatment device has at least two sub-devices or modules. A laser deviceL emits the laser beam 2 to the eye 3. The laser device L in this caseoperates fully automatically, i.e. the laser device L starts, on acorresponding start signal, to shift of the laser beam 2 and generatesin this manner cut faces which are constructed in a manner to bedescribed hereinafter and isolate a volume in the cornea of the eye. Thelaser device L receives beforehand via control lines which will not bedesignated in greater detail from a planning device P control datarequired for operation as a set of control data. The transmission takesplace before operation of the laser device L. It is of course alsopossible to communicate wirelessly. As an alternative to directcommunication, it is also possible to arrange the planning unit Pspatially separated from the laser unit L and to provide a correspondingdata transmission channel.

For example, the set of control data is transmitted to the treatmentdevice 1 and, also preferably, an operation of the laser device L isblocked until a valid set of control data is present on the laser deviceL. A valid set of control data may be a set of control data which is inprinciple suitable for use with the laser device L of the treatmentdevice 1. In addition, validity can also be linked to further testsbeing passed, for example whether particulars, which are additionallyfiled in the set of control data, about the treatment device 1, forexample a device serial number, or about the patient, for example apatient identification number, correspond to other particulars whichwere for example read out from the treatment device or separately inputas soon as the patient is in the correct position for operation of thelaser device L.

The planning unit P generates the set of control data, which is providedto the laser unit L for executing the surgical operation, frommeasurement data and defective vision data which were acquired for theeye to be treated. They are supplied to the planning unit P via aninterface S and originate in the illustrated example embodiment from ameasuring device M which previously measured the eye of the patient 4.Of course, the measuring device M can transmit the correspondingmeasurement and defective vision data to the planning unit P in anydesired manner.

The data can be transmitted by means of memory chips (for example by aUSB or memory stick), magnetic memories (for example floppy disks), byradio (for example WLAN, UMTS, Bluetooth) or in a hard wired manner (forexample USB, FireWire, RS232, CAN Bus, Ethernet, etc.). Of course, thesame applies with regard to the transmission of data between theplanning unit P and laser device L.

A direct radio or wired connection of the measuring device M to thetreatment device 1 with regard to the transmission of data, which can beused in a variant, has the advantage that the use of false measurementand defective vision data is ruled out with maximum possible certainty.This applies in particular when the patient is transferred from themeasuring device M or measuring devices to the laser device L by meansof a bed device (not shown in the figure) which interacts with themeasuring device M or the laser device L in such a way that therespective devices detect whether the patient 4 is in the properposition for measuring or introducing the laser radiation 2. In thiscase, the measurement and defective vision data can be transmitted tothe treatment apparatus 1 at the same time as the patient 4 istransferred from the measuring device M to the laser device L.

Suitable means can ensure that the planning unit P always generates theset of control data pertaining to the patient 4 and the risk of anerroneous use of an incorrect set of control data for a patient 4 is allbut ruled out.

The effect of the laser beam 2 is indicated schematically in FIG. 2. Thetreatment laser beam 2 is focused into the cornea 5 of the eye 6 bymeans of optics which are not be designated. This produces in the cornea5 a focus which covers a spot 6 and in which the laser radiation energydensity is so high that a non-linear effect occurs in the eye incombination with the pulse length. For example, each pulse of the pulsedlaser radiation 2 can generate at the respective spot 6 an opticalbreakthrough in the cornea 5 of the eye, which breakthrough in turninitiates a plasma bubble indicated schematically in FIG. 2. As aresult, tissue is separated in the cornea 5 by this laser pulse. When aplasma bubble is produced, the tissue layer separation comprises alarger area than the spot 6 which the focus of the laser radiation 2covers, although the conditions for generating the breakthrough areachieved only in the focus. In order for an optical breakthrough to begenerated by each laser pulse, the energy density, i.e. the fluence ofthe laser radiation, must be above a certain, pulse length-dependentthreshold value. This relationship is known to the person skilled in theart from DE 69500997 T2, for example.

Alternatively, a tissue-separating effect of the pulsed laser radiationcan also be generated in that a plurality of laser radiation pulses areemitted in a region, the spots 6 overlapping for a plurality of laserradiation pulses. A plurality of laser radiation pulses then co-operateto achieve a tissue-separating effect.

However, the type of tissue separation which the treatment device 1 usesis not relevant for the following description; all that matters is thattreatment laser radiation 2 pulsed is used. For example, use may be madeof a treatment device 1 such as is described in WO 2004/032810 A2. It isalso essential that a large number of laser pulse foci form a cut facein the tissue, the shape of which is dependent on the pattern in whichthe laser pulse foci are/become arranged in the tissue. The patternpredefines target points for the position of the focus, at which pointsone or more laser pulse(s) is/are emitted, and defines the shape andposition of the cut face. The pattern of the target points is importantfor the methods and apparatuses described on hereinafter and the patternwill be described in greater detail below.

In order now to execute a correction of defective vision, material isremoved from an area within the cornea 5 by means of the pulsed laserradiation by separating the layers of tissue which isolate the materialand then allow the material to be removed. The removal of materialeffects a change in volume in the cornea resulting in a change in theoptical imaging effect of the cornea 5, the dimensions of which areprecisely such that the previously determined defective visionis/becomes thereby corrected as far as possible. For isolating thevolume to be removed, the focus of the laser radiation 2 is directedtoward target points in the cornea 5, generally in a region positionedbelow the epithelium and the Bowman's membrane and also above theDescemet's membrane and the endothelium. For this purpose, the treatmentdevice has a mechanism for shifting the position of the focus of thelaser radiation 2 in the cornea 5. This is shown schematically in FIG.3.

Elements of the treatment device 1 are included in FIG. 3 only in so faras they are required to understand the shifting of the focus. The laserradiation 2 is, as mentioned hereinbefore, focused to a focus 7 in thecornea 5, and the position of the focus 7 in the cornea is shifted, sothat for generating the cut face at various points focused energy fromlaser radiation pulses is introduced into the tissue of the cornea 5.The laser radiation 2 is provided as pulsed radiation by a laser 8. Anxy scanner 9, which is embodied in a variant by two galvanometer mirrorsdeflecting about substantially orthogonally axes, two-dimensionallydeflects the laser beam coming from the laser 8, so that after the xyscanner 9 a deflected laser beam 10 is present. The xy scanner 9 thuseffects a shifting of the position of the focus 7 substantiallyperpendicularly to the main direction of incidence of the laserradiation 2 into the cornea 5. In addition to the xy scanner 9, a zscanner 11, which is embodied as an adjustable telescope for example, isprovided for adjusting the depth position. The z scanner 11 provides forthe z position of the focus 7, i.e. the position thereof on the opticalaxis of incidence, being shifted. The z scanner 11 can be arrangeddownstream or upstream of the xy scanner 9. The coordinates denotedhereinafter by x, y, z therefore relate to the shifting of the positionof the focus 7.

The allocation of the individual coordinates to the spatial directionsis not essential for the functioning principle of the treatmentappliance 1; however, for the sake of simplicity of description, zdenotes hereinafter in all cases the coordinates along the optical axisof incidence of the laser radiation 2, and x and also y denote twomutually orthogonal coordinates in a plane perpendicular to thedirection of incidence of the laser beam. The person skilled in the artis of course aware that the position of the focus 7 in the cornea 5 canalso be three-dimensionally described in other coordinate systems; inparticular, the coordinate system does not have to be a system ofrectangular coordinates. The fact that the xy scanner 9 deflects aboutaxes at right angles to one another is therefore not compulsory; on thecontrary, use may be made of any scanner which is able to adjust thefocus 7 in a plane in which the axis of incidence of the opticalradiation does not lie. Systems of oblique coordinates are thus alsopossible.

Furthermore, systems of non-rectilinear coordinates can also be used todescribe or control the position of the focus 7, as will also becommented on hereinafter in greater detail. Examples of coordinatesystems of this type are spherical coordinates and also cylindricalcoordinates.

For controlling the position of the focus 7, the xy scanner 9 and alsothe z scanner 11, which jointly form a specific example of athree-dimensional focus shifting device, are activated by a controller12 via lines which are not designated. The same applies to the laser 8.The controller 3 ensures a suitably synchronous operation of the laser 8and also of the three-dimensional focus shifting device, implemented inexemplary fashion by the xy scanner 9 and also the z scanner 11, so thatthe position of the focus 7 in the cornea 5 is shifted in such a waythat ultimately a material of specific volume is isolated, thesubsequent removal of volume effecting a desired correction of defectivevision.

The controller 12 operates in accordance with predefined control datawhich define the target points for the focus shifting. The control dataare generally summarised in a set of control data. In one embodiment,the set of control data defines the coordinates of the target points asa pattern, wherein the sequence of the target points in the set ofcontrol data defines the sequential arrangement of the focus positionsand thus ultimately a path curve (referred to in the present documentalso as a path for short). In one embodiment, the set of control datacontains the target points as specific setting values for the focusposition shifting mechanism, for example for the xy scanner 9 and the zscanner 11. For preparing the ophthalmic surgical method, i.e. beforethe actual surgical method is executed, the target points and preferablyalso the order thereof are determined in the pattern. The surgicalintervention must be pre-planned in such a way that the control data forthe treatment device 1 are defined, the application of which data thenachieves a correction of defective vision that is optimal for thepatient 4.

The first step is to define the volume which is to be isolated from thecornea 5 and subsequently to be removed. As previously described withreference to FIG. 1a , this requires the need for correction to beascertained. FIG. 4 shows in subfigures a), b) and c) the opticalconditions in the eye 3 of the patient 4. Without defective visioncorrection, the situation is that shown in subfigure a). The cornea 5effects together with the lens 13 of the eye a focusing of an objectlying at infinity into a focus F positioned on the z axis after theretina 14. The imaging effect derives in this case on the one hand fromthe lens 13 of the eye, which lens is relaxed when the eye is notaccommodated, and also on the other hand from the cornea 5 of the eyethat is defined substantially by a front face 15 of the cornea and alsoa back 16 of the cornea and likewise has an imaging effect on account ofits curvature. The optical effect of the cornea 5 is caused by theradius of curvature R_(CV) of the front surface of the cornea. Subfigurea) represents the defective vision merely in exemplary fashion; inreality, the above-mentioned more complex defective visions may bepresent. However, the following description applies to them too,although some of the specified equations may then contain an additionalangle dependency even if reference is not expressly made thereto.

For correcting defective vision, a front lens 17 in the form of a pairof spectacles is placed in a known manner, as illustrated in subfigureb) of FIG. 4, before the eye 3 at a distance d_(HS) from the vertex ofthe cornea 5. The refractive power B_(BR) of the lens 17 is adapted suchthat the lens shifts the far point of the system as a whole, i.e. thesystem made up of the pair of spectacles and eye, from the focus point Fto the corrected focus point F* which is positioned on the retina 14.

With regard to the nomenclature used in this description, it should benoted that the addition of an asterisk to variables indicates that theyare variables obtained after a correction. The focus F* is thereforethat focus which is present after the optical correction which isachieved in subfigure b) of FIG. 4 by the lens 17 of the pair ofspectacles.

Under the justified assumption that a change in thickness of the cornea5 mainly modifies the radius of curvature of the air-facing anteriorsurface 15 of the cornea, but not the radius of curvature of theposterior surface 16 of the cornea facing the interior of the eye, theradius of curvature R_(CV) of the anterior surface 15 of the cornea ismodified by the removal of the volume. The cornea 5 reduced by thevolume has an imaging effect which is altered in such a way that thefocus F*, which is then corrected, lies on the retina 14. After thecorrection an altered anterior surface 15* of the cornea is present, anda correction of defective vision is achieved even without a pair ofspectacles.

The curvature to be achieved of the modified anterior surface 15* of thecornea is therefore determined for defining the pattern of the targetpoints. In this case, the starting point is the refractive power of thelens 17 of the pair of spectacles, as determining the correspondingparameters is a standard method in ophthalmic optics. The followingformula applies to the refractive power B_(BR)(φ) of the lens 17 of thepair of spectacles:

B _(BR)(φ)=Sph+Cyl·sin²(φ−θ).  (1)

In this equation Sph and Cyl denote the correction values to beimplemented of spherical and astigmatic refractive defects respectivelyand θ denotes the position of the cylinder axis of the cylindrical(astigmatic) defective vision, such as they are known to the personskilled in the art in optometry. Finally, the parameter φ refers to asystem of cylindrical coordinates of the eye and is countedanticlockwise looking onto the eye, such as is conventional inophthalmic optics. Now, with the value B_(BR), the curvature of themodified anterior surface 15* of the cornea is set as follows:

R _(CV)*=1/((1/R _(CV))+B _(BR)/((n _(c)−1)·(1·d _(HS) ·B_(BR))))+F  (2)

In Equation (2) n_(c) denotes the refractive index of the material ofthe cornea. The respective value is usually 1.376; this denotes thedistance at which a pair of spectacles having the refractive powerB_(BR) must be positioned from the corneal apex in order to generate thedesired correction of defective vision by means of the pair ofspectacles; B_(BR) denotes the aforementioned refractive power of thepair of spectacles according to Equation (1). The indication for therefractive power B_(BR) can also include defective visions extendingbeyond a normal spherical or cylindrical correction. B_(BR) (and thusautomatically also R_(CV)*) then have additional coordinatedependencies.

The correction factor F takes account of the optical effect of thechange in thickness of the cornea and may be regarded in the firstapproximation as a constant factor. For a high-precision correction, thefactor can be calculated in accordance with the following equation:

F=(1−1/n _(c))(d _(C) *−d _(C)).  (3)

d_(C) and d_(C)* are in this case the thickness of the cornea before andafter the optical correction respectively. For precise determination,R_(CV)* is calculated iteratively in that in the i^(th) calculation thevariable (d_(C)*−d_(C)) is concluded from the difference(R_(CV)*−R_(CV)) and the corresponding result obtained therefrom for thechange in thickness is applied in the (i+1)^(th) calculation. This canbe carried out until a termination criterion is met, for example if thedifference of the result for the change in thickness is in twosuccessive iterations steps below a correspondingly defined limit. Thislimit can be defined via a constant difference, for example,corresponding to a precision of the refractive correction that isappropriate for the treatment.

If the change in thickness of the cornea of the eye is disregarded (asis entirely permissible for a simplified method), the correction value Fin Equation (2) can be set to zero for a simplified calculation, i.e.disregarded and omitted. Surprisingly, the following simple equation isobtained for the refractive power of the modified cornea 5*:

B _(CV) *=B _(CV) +B _(BR)/(1−B _(BR) ·d _(HS))

This equation provides the person skilled in the art in a simple manner,by means of the equation B_(CV)*=(n−1)/R_(CV)*, with the radius R_(CV)*of the anterior surface 15* of the cornea that must be present after themodification in order to obtain the desired correction of defectivevision, as follows:R_(CV)*=1/((1/R_(CV))+B_(BR)/(n_(c)−1)·(1−d_(HS)·B_(BR)))).

For the volume, the removal of which effects the foregoing change incurvature of the anterior surface 15 of the cornea, the border faceisolating the volume is now defined. In this regard, account mustpreferably be taken of the fact that the diameter of the region to becorrected, and thus the diameter of the volume to be removed, should ifpossible extend over the size of the pupil of the dark-adapted eye.

In a first variant, numerical methods known to the person skilled in theart are used to define a free face circumscribing a volume, removal ofwhich effects the change in curvature. For this purpose, the change inthickness required for the desired modification of curvature isdetermined along the z axis. This provides the volume as a function ofr, y (in cylindrical coordinates) and this in turn provides the borderface thereof.

A simple analytical calculation leads to the following second variant inwhich the border face of the volume is constructed by two face parts: ananterior face part facing the surface 15 of the cornea and an opposingposterior face part. FIG. 5 shows the corresponding conditions. Thevolume 18 is bounded towards the anterior surface 15 of the cornea by ananterior cut face 19 positioned at a constant distance d_(F) below theanterior surface 15 of the cornea. This anterior cut face 19 is alsoreferred to, by analogy with a laser keratome, as a flap face 19, as itserves to allow in the cornea 5 of the eye a lamella in the form of aflap to be lifted, in combination with an opening cut toward the edge,from the underlying cornea 5. This type of removal of the previouslyisolated volume 18 is of course also possible here.

The anterior cut face 19 has a course of curvature which is positionedby d_(F) below the anterior surface 15 of the cornea. If the anteriorsurface is spherical during the surgery, a radius of curvature which isless than the radius of curvature R_(CV) by d_(F) can be specified forthe flap face 19. As will be described hereinafter for preferredvariants, a contact glass can ensure when generating the cut face 19that the anterior surface 15 of the cornea is spherical at the momentwhen the cut face is generated, so that the pattern of the target pointsgenerates a spherical cut face. Although the relaxation of the eye 3after the detachment of the contact glass may then lead to anon-spherical cut face 19, it is still at a constant distance from theanterior surface 15 or 15* of the cornea.

Posteriorly, the volume 18 which is to be removed from the cornea 5 isbounded by a posterior cut face 20 which is generally not at a constantdistance from the anterior surface 15 of the cornea. The posterior cutface 20 will therefore be embodied in such a way that the volume 18 hasthe form of a lenticule, for which reason the posterior cut face 20 isalso referred to as the lenticule face 20. In FIG. 5 the posterior cutface is illustrated, by way of example for a correction of myopia, as alikewise spherical face having a radius of curvature R_(L), wherein thecentre of this curvature generally does not coincide with the centre ofcurvature of the anterior surface 15 of the cornea, which is likewisespherical in FIG. 5. In a correction of hyperopia, R_(L) is greater thanR_(CV)−d_(F).

FIG. 6 shows the conditions after removal of the volume 18. The radiusof the modified anterior surface 15* of the cornea is now R_(CV)* andcan be calculated in accordance with the equations describedhereinbefore, for example. The central thickness d_(L) of the removedvolume 18 is in this case decisive for the change in radius, as FIG. 7illustrates. In this figure the height h_(F) of the spherical capdefined by the anterior cut face 19, the height h_(L) of the sphericalcap defined by the posterior cut face 20, and also the thickness d_(L)of the volume 18 to be removed are also indicated as further variables.

The posterior cut face 20 defines, on account of the constant distancebetween the anterior surface 15 of the cornea and the anterior cut face19, the course of curvature of the anterior surface 15* of the corneaafter removal of the volume 18. Thus, the posterior cut face 20 willhave an angle-dependent radius of curvature, for example in a correctionof defective vision taking into account cylindrical parameters. For thelenticule face 20 shown in FIG. 7, the following generally applies:

R _(L)(φ)=R _(CV)*(q)−d _(F),

or in cylindrical coordinates (z, r, φ)

z _(L)(r,φ)=R _(L)(φ)−(R _(L) ²(φ)−r ²)^(1/2) +d _(L) +d _(F).

When not taking account of an astigmatism, the dependency on y isdispensed with and the lenticule face 20 is spherical. However, startingfrom the need for a cylindrical correction of defective vision, thelenticule face 20 generally has different radii of curvature on variousaxes, the radii of curvature mostly having the same vertex of course.

Furthermore, this automatically makes it clear that, in the case of amyopic cylindrical correction, the theoretical line of intersectionbetween the flap face 19 and lenticule face 20 does not lie in oneplane, i.e. at constant z coordinates. The smallest radius of curvatureof the lenticule face 20 is at φ=θ+π/2; the largest is of course on theaxis θ of cylindrical defective vision, i.e. at φ=θ. Unlike in theillustration of FIG. 7, in a correction of defective vision, thevertices of the flap face 19 and lenticule face 20 theoreticallycoincide and the lenticule face 20 is curved more intensively than theflap face 19. The thickness d_(L) of the lenticule is obtained as thecentral lenticule thickness in myopia.

In the case of the correction of myopia, the volume 18, which is to beregarded as a lenticule, theoretically has a line of intersection of thelenticule face 20 and flap face 19 at the edge. In the correction ofhyperopia, a finite edge thickness is always provided, as the lenticuleface 20 is curved less intensively than the flap face 19. However, inthis case, the central lenticule density is theoretically equal to zero.

In addition to the flap face 20 and the lenticule face 19, an additionaledge face is provided that bounds the bounded volume 18 of the flap face20 and the lenticule face 19 at the edge. The cutting of this edge faceis also executed using the pulsed laser beam. The structure of the edgeface will be described hereinafter with reference to FIGS. 12a -c.

The embodiment shown in the figures of the volume 18 as being bounded byan anterior cut face 19 at a constant distance from the front face 15 ofthe cornea and also a posterior cut face 20 is just one option forbounding the volume 18. However, it has the advantage that the opticalcorrection is defined substantially by just one face (the lenticule face20), so that the analytical description of the other face part of theborder face is simpler.

Furthermore, optimum safety margins are provided with regard to thedistance of the volume from the anterior surface 15 of the cornea andthe posterior surface 16 of the cornea. The remaining thickness d_(F)between the anterior cut face 19 and the anterior surface 15 of thecornea can be set to a constant value of from 50 to 200 μm, for example.In particular, it can be selected in such a way that the pain-sensitiveepithelium remains in the lamella formed by the flap face 19 below theanterior surface 15 of the cornea. The formation of the spherical flapface 19 is also in line with previous keratometer cuts; this isadvantageous for the acceptance of the method.

After generating the cut faces 19 and 20, the volume 18 thus isolated isthen removed from the cornea 5. This is schematically represented inFIG. 8 which further shows that the cut faces 19 and 20 are generatedunder the action of the treatment laser beam incident in a focus cone21, for example by sequential arrangement of plasma bubbles, so that ina preferred embodiment the flap cut face 19 and the lenticule cut face20 are generated by suitable three-dimensional shifting the focusposition of the pulsed laser radiation 2.

However, alternatively, in a simplified embodiment it is possible formerely the flap face 19 to be formed by target points defining thecurved cut face 19 at a constant distance from the anterior surface 15of the cornea by means of pulsed laser radiation and for the volume 18to be removed by laser ablation, for example using an excimer laserbeam. For this purpose, the lenticule face 20 can be defined as a borderface of the removal, although this is not mandatory. The treatmentdevice 1 then works like a known laser keratome; nevertheless, the cutface 19 is generated on a curved cornea. The features describedhereinbefore and hereinafter respectively are also possible in suchvariants, in particular as far as the determination of the boundaryface, its geometric definition and the determination of controlparameters is concerned.

If both the lenticule face 20 and the flap face 19 are generated bymeans of pulsed laser radiation, it is expedient to form the lenticuleface 20 before the flap face 19, as the optical result in the lenticuleface 20 is better (or even may be achieved only) if no alteration of thecornea 5 has yet occurred above the lenticule face 20.

The removal of the volume 18 isolated by the pulsed laser radiation canbe achieved, as indicated in FIG. 8, by an edge cut 22 allowing thevolume 18 to be extracted in the direction of an arrow 23 shown in FIG.8. However, alternatively, the edge cut 22 can be embodied in such a waythat it connects the anterior cut face 19, i.e. the flap face 19, in theform of a ring to the anterior surface 15 of the cornea, although theedge cut does not extend all the way round an angle of 360°. The lamellaisolated in this way remains connected to the remaining tissue of thecornea 5 in a narrow region. This connecting bridge then serves as ahinge, so as to be able to fold the otherwise isolated lamella away fromthe cornea 5 and to detach the already isolated volume 18 madeaccessible in this manner from the remainder of the cornea 5 of the eye.The position of the connecting bridge can be predefined when generatingthe control data or the target points respectively. From this point ofview, the described procedure or device therefore isolates the volume 19within the cornea 5 and generates a lamella, connected to the remainderof the cornea of the eye via a tissue bridge, as a lid over the volume.The lid can be folded away and the volume 18 can be removed.

To generate the cut faces 19 and 20, the target points can now bearranged in a broad range of ways. The prior art, for example WO2005/011546, describes how special spirals, which extend for example inthe manner of a helical line about a main axis lying substantiallyperpendicularly to the optical axis (z axis), can be used to generatecut faces in the cornea of the eye. The use of a scanning pattern, whicharranges the target points in lines, is also known (cf. WO 2005/011545).It goes without saying that these options can be used to generate theabove-defined cut faces.

The edge face mentioned hereinbefore may be seen in greater detail inFIGS. 9a and 9b . Elements which have already been described withreference to other figures are provided in these figures with the samereference numerals, so that they will not necessarily be describedagain.

FIG. 9A is a plan view onto the anterior surface 15 of the cornea withthe flap face 19 and also the lenticule face 20 (the rim of which isindicated by a dashed line) and also the edge cut 22 in the case of acorrection of hyperopia. A zone of transition between the edge of thelenticule face 20 and the flap face 19, which is achieved by an edgeface 24, may also be seen in FIG. 9A. This edge face 24 may clearly beseen in FIG. 9B which is a sectional illustration through theillustration of FIG. 9A along the lines A-A.

The edge face 24 effects the transition from the lenticule face 20 tothe flap face 19. In this case, it is designed in the embodiment of FIG.9B as a conical face which is positioned more obliquely than a conical(in the plan view onto FIG. 9A) face, which is oriented perpendicularlyto the front face 15 of the cornea or to the flap face 19 extendingparallel thereto, would be positioned. The edge cut 22 is positioned atan angle α to the axis of vision OA, which angle results in suchperpendicular course relative to the front face of the cornea.

On the other hand, the edge face 24 extends in a more inclined manner,so that the width B, which the edge face 24 has when viewed from aboveand along in the direction of the optical axis OA, is greater than inthe edge cut 22, for example. The corresponding angle β is accordinglyalso larger than the angle α.

FIGS. 10A and 10B show the corresponding conditions in the case of amyopic lenticule, i.e. in the correction of myopia. In this case too,the edge face 24 is provided for and leads to a finite edge thickness ofthe lenticule 18 that would not be provided in itself on account of thelarger curvature of the lenticule face 20 compared to the flap face 10,as both faces would have, at least in their continuation, a line ofintersection, i.e. the edge would end in a line of intersection.

The minimum thickness of the lenticule 18, which is present, in ahyperopic form according to FIG. 9B, on or close to the optical axis OA,occurs therefore in a myopic lenticule according to FIG. 10B at theedge. Accordingly, the minimum thickness d_(M) is also shown at the edgein FIG. 10B.

It goes without saying that the sectional illustrations of FIGS. 9B and10B are descriptive for the lenticule as a whole only when nohigher-order correction, in particular no astigmatism, is present. Ifthere is astigmatism, the lenticule face 20 is corrected accordingly soas to differ from sphericity; this also has an effect on the edge face24 in a manner which is obvious to the person skilled in the art.

Finally, FIGS. 11A and 11B show conditions corresponding to those ofFIGS. 9a and 9b ; however, in this case, the edge cut 22, which isgenerated to expose the lenticule 18, extends over a very much largerangular range than in FIGS. 9 and 10.

FIGS. 9 to 11 show an edge face 24 which is designed as an oblique cut.However, the edge face 24 can also have a structure differing from sucha course which is linear viewed in cross section. This is shown by wayof example in FIGS. 12A to 12D. In these figures, FIG. 12A represents asectional illustration similar to that of FIG. 9B, 10B or 11B. FIGS. 12Bto 12D are enlarged views of the detail indicated by a dotted line inFIG. 12A and represent different options for the structure of the edgeface 24.

According to FIG. 12B the edge face 24 consists of two portions 25 and26 which are substantially linear in cross section. The first portion 25runs perpendicularly into the flap face 19. The height of the firstportion 25 effects a thickness d_(R) of the edge. This thickness ispreferably selected so as to be in the range of from 5 to 10 μm andensures that fragments do not become torn off in the region of the edgeface 24 when the lenticule 18 is removed. Such fragments would have verydisadvantageous effects on ingrowth and would lead to undesirableregression. In order to achieve, despite the first portion 25 lyingperpendicularly to the flap face 19, a smooth positioning of the corneallamella 27 isolated by the flap cut 19 when the lenticular volume wasremoved, the second portion 26 of the edge face 24 has in the embodimentof FIG. 12b an oblique course towards the axis of vision. This obliquecourse provides, in turn, a width B which is much greater than thatwhich would be provided in an edge 24 extending perpendicularly to theflap face 19 throughout.

FIG. 12C shows a modification of the structure of the edge face 24 ofFIG. 12B, in which a continuously curved second portion 26, which roundsoff the edge between the lenticule face 20 and the flap face 19 in theregion remote from the anterior surface 15 of the cornea of the eye, isformed on the first portion 25 running perpendicularly into the flapface 19. The perpendicular running-in of the first portion 25 ensures,again, a minimum edge thickness d_(R) which prevents pieces of tissuefrom becoming torn off from the edge of the lenticule when thelenticular tissue is removed.

This is also achieved in the edge structure according to FIG. 12D, whichis embodied in an S-shaped manner, the first portion 25 running, again,perpendicularly into the flap face 19. On account of the S-shapedstructure, the sectional illustration of the edge face 24 has in thisconfiguration a turning point, and the second portion 26 preferably endslikewise at right angles in the lenticule face 20.

The contact glass has the further advantage that the anterior surface 15of the cornea is also automatically spherical as a result of thepressing onto the spherical underside 26 of the contact glass. Thus,when the contact glass is pressed on, the anterior cut face 19, which ispositioned at a constant distance below the anterior surface 15 of thecornea, is also spherical, leading to a greatly simplified control. Itis therefore preferable, quite independently of other features, to use acontact glass having a spherical contact glass underside and to boundthe volume by an anterior cut face 19 and also a posterior cut face, theanterior cut face being generated as a spherical face at a constantdistance d_(F) below the anterior surface 15 of the cornea. Theposterior cut face has a course of curvature corresponding, apart fromthe distance d_(F) from the anterior surface of the cornea, to thatdesired for the correction of defective vision when the eye is relaxed,i.e. after the contact glass has been detached. The same applies to thedefinition of the target points and to the operating methodrespectively.

1. A treatment apparatus for surgical correction of hyperopia in an eye(3), the treatment apparatus (1) having a laser device (L) which iscontrolled by a control device (12) and separates corneal tissue byapplying laser radiation (2), the control device (12) being embodied tocontrol the laser device (I) for emitting the laser radiation (2) intothe cornea (5) in such a way that a lenticular volume (18) is isolatedin the cornea (5), the removal of which volume effects a desiredcorrection of hyperopia, characterised in that the control device (12),when controlling the laser device (L) defines the lenticular volume (18)during to have a posterior face (20) and an anterior face (19), theedges of which are connected via an annular edge face (24), the edgeface (24) having in projection along an axis of vision (OA) of the eye aring width (B) which is greater than that which would have in the sameprojection a straight line which is perpendicular at the edge of theposterior or the anterior face (20, 19) on the respective face andconnects the anterior face (19) to the posterior face (20) or to anotional continuation thereof.